The present invention relates in general to apparatus for, and a method of driving tunnels, galleries, adits, trenches and similar excavations referred to hereinafter for convenience as tunnels. More particularly, the present invention is concerned with drive shield for tunnelling apparatus and to a method of forming a permanent lining for a tunnel.
It is known to drive tunnels with the aid of drive shields composed of a series of elongate drive members or knives supported and guided for individual displacement on a frame. Rams serve to alternately advance the drive members and the frame. It is also known to provide the individual drive members with follow-up tails which form a rear shield to support the tunnel wall between the forward drive shield and a permanent rear lining. To create the permanent lining, fluid concrete can be introduced into the rear shield and the rear shield can then form a sheath or form for the concrete. A main inner form conveniently composed of removal cylindrical parts can be spaced from the rear shield to define the radially-innermost surface of the concrete reception space. The individual parts of the inner form can then be repositioned successively as the tunnel progresses. A further wall is also provided to delimit the front end of the concrete receptive space. This further wall is usually a simple sheet or plate attached or engaged with the main inner form at its forward end and engaging on the inner surface of the rear tails to thereby seal off the reception space. It is also known to profile or shape the rear tails to create stiffness and resist flexure and in this case the further wall must be adapted to conform with such a shaping to thereby maintain its sealing effect. Despite such measures however it is quite common for the drive shield to deviate from the intended path of the tunnel and consequently the relative positions between the rear shield and the main form can vary. As a result the further wall cannot reliably seal off the concrete and the only recourse is to utilize a fresh wall for each concrete section especially adapted to the particular positional relationship between the outer sheath, i.e., the rear shield, and the main inner form. With regard to the foregoing the present invention seeks to provide an improved construction for the rear shield components and an improved method for forming the concrete lining for the tunnel.